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Users are complaining that EMC's Mozy backup service is mistakenly backing up complete data sets over and over again. According to posts in five-page Mozy Forum thread, the problem has been present since mid-June, and users say they've received inadequate support.

The problem occurs with Mozy for Windows. According to users, the service repeatedly backs up data to Mozy servers in the cloud, and causes affected computers to run normal applications slowly. "[The problem] started with me needing to re-install the client due a problem with my operating system," one user tells us. "When the automated backup started the Mozy client decided it was going to re-upload all 65GB of my backed up files from scratch, despite them not being changed in any way and the backed up versions on the server still being visible and available for restore."

According to this user, an EMC support rep denied the problem. "Despite me confirming that the Mozy client was actually re-uploading the files, support have told me twice that it is just doing a version check and not actually uploading at all."

Asked about the issues, an EMC spokesperson said that the service is not doing repeat backups. "Once in a while, Mozy may run a full back up as part of an integrity verification," the spokesperson said. "But this happens rarely. Most of the time Mozy appears to be backing up when it is merely checking to see if files marked for back up on the customer's machine are the same as the files we have on our servers. This checking process happens more frequently for customers who are backing up data from external hard drives.

"To the customer, Mozy may look as though it is backing up data again when really Mozy is checking to see if the files we have on our servers match what the customer has on his or her machine."

The thread on Mozy's support forum started on 10 June. "Recently my cable from my HD came loose and now Mozy is backing up ALL of my data from scratch again," reads the first post. "Yes, I know it might appear that it is starting from the beginning and really not backing up all, but it is indeed transferring files that are old, never changed and already backed up from before."

The poster was backing up from an internal drive, using a paid subscription to Mozy Home, and using Mozy's default encryption. Other posters on the forum, such as Pablo and Johnhboyd, chimed in saying it was happening to them too. The problem seems to occur with both V.2 and the older V 1.16.4.0 of Mozy. "I'm testing a competitor now, and while there were some problems, it seems to be working well after rebooting my machine," said poster RichardR.

The thread moderator removed the name of the competing product. And RichardR didn't like it. "Perhaps if Mozy would devote as much attention to fixing their problems as they did to editing my last post, I wouldn't need to be testing a specific competitor's product." Once again the name of the competing product was removed.

"Sorry Richard, we just don't allow the promotion of competitors on our boards," said Mozy Community manager Mike Jones. He then posted a diagnosis of the problem:

A couple of things could be going on here. A lot of people think the files are being re-backed up when really they are just being re-associated. This takes a little bit of time for the encrypting and comparing files to the servers files, but it is much faster than re-uploading. If the files are actually re-uploading then you either switched encryption keys, or the integrity check is asking for a rebase.

A rebase is where the file is uploaded from scratch to get rid of all of the patches and get a new original file. The way Mozy works is you upload the original file, then every time the file changes, a patch gets uploaded so the entire file doesn't have to be re-uploaded. If a file like an email .pst files (not all of your files) has tons of patches on it, the integrity check might tell it to re-upload to be safe.

But this didn't apply to poster Mikee. "My external drive USB got disconnected. I didn't notice for about a week," he said. "It appears that Mozy decided that I didn't want the files on this drive backed up anymore and it removed them all. What if the drive had died? It looks like I would have lost everything. This makes Mozy pretty much useless. I need to find another service. I wonder if I can get my money back since it appears that I have never really had any security with this service."

Mozy will delete backup up files if the source hard drive is switched off for 30 days. Poster twirlerzmom said his external drive was only disconnected for 20 minutes.

"I appreciate your support here, but you absolutely don't know what you are talking about," Johnhboyd said in response to Mike Jones' post. "I have sat at my computer and watched it upload 7+ GB of files that haven't changed in months."

Also other users said the re-indexing and re-synching appears to take just as long as an actual backup. Mozy support staff admitted there had been load-balancing problems with some of their servers. "There was some sort of Mozy Server error on the Mozy log, and it started a new full backup anew," said poster llua001. "It's been going for more two full days now, day-and-night. And it is a backup for sure, not a re-association."

The problem has occurred with v1.06, v 2.2.0.6 and v2.0.12.3 of Mozy. The latest posts indicate things are getting better and that problems on Mozy's servers were the cause of the repeated full backups.

EMC says it's working to minimize the alleged repeat backups, saying that the latest release, 2.2, includes several improvements that should help. ®